I would have to assume that a 105K BTU heater would make a difference, but that is just a guess.
I can help with the run time though.
Propane has roughly 91,600 BTU/gallon. So for lets figure the run time of the standard BBQ grill bottle (20 lb.), they hold right at 4.73-gallons.
4.73-gallon x 91,600 BTU/gallon = 433,000 BTU capacity for one 20 lb. BBQ tank.
If the heater burns 105,000 BTU/hour on high, then we have...
433,000 BTU / 105,000 BTU/hour = 4.1 hours. (not very long)
They sell the propane tanks in 20, 30, 80, and 100 lb. sizes.
Obviously the bigger the tank the longer the run time. A 100 lb. tank like
this one runs about $130 and will run the heater for 20.6 hours.
Now all of that is assuming you have it on high all the time. If you run it at half of full output, then your run times will double. I would think you would need high to warm the water then drastically less to keep it at that temp.